So we've got the old computer, and it's got FireWire ports on it to support an iPod. We've got this Comcast Motorola 6412 DVR with a firewire port on the back. There are WinXP drivers for the digital tuner interface that DVD recorders can use to record data off the AV stream.
So, what the hell, it's worth a try.
I configured remote desktop on the old computer, moved it into the living room (where it's headless) and plugged it into the router that's sitting behind the TV. So far, so good.
Uninstalled a bunch of the old software on the machine. Upgraded iTunes and plugged the audio line out into the stereo. Figured out how to make remote desktop not capture the audio output to the client machine. So I've got a remote playback device in the living room now, and didn't have to spend $200 on a Roku SoundBridge.
Plugged in the firewire cable.
No auto detection wizard came up, but I was on remote desktop, so that might have wonked things up. Got the device through the "Add new hardware" panel and installed the drivers.
Drivers wouldn't start the device properly. May also have been a side-effect of trying to work through remote desktop.
Fiddled a bit, and eventually decided I didn't really care. The drivers are only good for recording real-time, not for snagging data files off the DVR's drive. While that's cool in that it can record video-on-demand programming that the DVR can't, it doesn't help me deal with the hours and hours of programming I might want to save in an efficient manner. Oh, well.